Quantum computing is a class of computing in which inherently quantum mechanical phenomena, such as quantum state superposition and entanglement, are harnessed to perform certain computations far more quickly than any classical computer could ever be capable of. In a “topological” quantum computer, calculations are performed by manipulating quasiparticles—called “non-abelian anyons”—that occur in certain physical systems. Anyons have unique physical characteristics that distinguish them from both fermions and bosons. Non-abelian anyons also have unique properties with respect to abelian anyons. It is these unique properties that serve as a basis for topological quantum computing, in which information is encoded as a topological property of non-abelian anyons; specifically the braiding of their space-time worldlines. This has certain benefits over other models of quantum computation. One key benefit is stability, as the quantum braiding is unaffected by perturbations on a scale that could cause error-inducing quantum decoherence in other types of quantum computer.
Broadly speaking, to date, two types of physical system have been considered as potential hosts of non-abelian anyons, namely “5/2 fractional quantum Hall” systems in condensed matter physics, and (more recently) semiconductor-superconductor (SM/SC) nanowires. Regarding the latter, a key advance in the field was the realization that non-abelian anyons, in the form of “Majorana zero modes” (MZMs) can be formed in semiconductor (SM) nanowires (NWs) coupled to a superconductor (SC).
One of the issues encountered in the context of SM/SC nanowires is the existence of so-called “soft gap” states. The soft gap issue has been documented in publicly-available literature, and suffice it to say that these soft gap states, when present, are a source of decoherence for the MZMs. Analysis and experiments indicate that a source of the soft gap is disorder in the SM/SC interface, and there has been recent work in the field on improving the quality of the SM/SC interface with the aim of providing more stable MZMs.